Many foraging insects locate flowers using their odour plumes which are comprised of a combination of chemicals called volatile organic compounds (VOCs). The characteristics of odour plumes can be altered by atmospheric pollutants, especially nitrogen dixoides and ozone, which can react with the plume or mask its components. The possible impacts on insect foraging are largely unknown.
Researchers in the UK conducted field studies to investigate whether diesel exhaust and ozone could affect the ability of pollinators to locate floral resources and provide pollination services. They found that elevating diesel exhaust and ozone, individually and in combination, resulted in dramatic reductions in the number of insect pollinators (62-70%) and flower visits (83-90%) (Figure 1). This was a result of the reduction in abundance of seven insect groups: all bees (i.e. honeybees, solitary bees and bumblebees), all flies (i.e. hoverflies and other flies), butterflies and moths. Three insect groups were not significantly affected: beetles, true bugs and parasitic wasps.
The reduction in flower visitation resulted in significant decreases in the seed metrics of black mustard plants (Brassica nigra cv. Abyssinica) in terms of the number of seeds per pod, pod mass and number of pods developed. This self-fertile variety was not reliant on pollination for seed development, and the results suggest that plant species more reliant on insect pollination may be more severely affected.
The researchers conclude that air pollutants reduce insect-provided pollination services, even at levels currently deemed to be safe for the environment by legislation. They call for more research to investigate the potential effects of air pollutants on insect-mediated ecological processes and ecosystem services.
Figure 1. The effects of diesel exhaust and ozone pollution on pollinator foraging behaviour. Means (±SE) of pollinator abundance (A), flower visitation frequencies (B), abundances per insect group (C) and flower visits per insect group (D) were scaled according to the number of flowers within each observation unit and survey duration. For part C, numbers in square brackets represent the total number of individuals counted for each group. If an insect landed on a flower within the observation unit, that insect was counted as ‘1’ for abundance. If that same insect landed on five flowers within the observation unit, the number of flower visits was recorded as ‘5’. Flower visitation (B and D) was recorded for bees, hoverflies, butterflies and moths only.
Copyright: Authors: Ryalls, J.M., Langford, B., Mullinger, N.J., Bromfield, L.M., Nemitz, E., Pfrang, C. and Girling, R.D. Publication: Environmental Pollution. Date: 2022. Licensed under CC BY 4.0https://creativecommons.org/licenses/by/4.0/ Source: Figure 2 https://www.sciencedirect.com/science/article/pii/S0269749122000616
Read the full paper:
Ryalls, J.M., Langford, B., Mullinger, N.J., Bromfield, L.M., Nemitz, E., Pfrang, C. and Girling, R.D., 2022. Anthropogenic air pollutants reduce insect-mediated pollination services. Environmental Pollution, 297, p.118847. https://doi.org/10.1016/j.envpol.2022.118847